Wednesday, August 3, 2016

Messing with output power - higher VCC

Messing with output power - higher VCC

So, tonight I decided to see if I could increase my output power by increasing the VCC of the board. By default, the Wisp1 is configured for VCC at 2.56 volts.  This generates an output signal at 1.9v Peak-2-Peak, or 9.02 milliwatts.

Now, in practice, there's no technical reason my board can't run at 3v3.  All of the components are certified up to 3.6 volts.

Poking around my parts box, I didn't have the correct resistors to modify the voltage divider for 3v3. However, I was able to boost it up from 2.56 to 2.98 volts.

Almost everything on my board is certified at 2.98 volts, with the exception of the Si5351 chip.  From the datasheet:

Technically, according to this table, the Si5351 requires 3.0 - 3.6v.  However, if you look at the note below, it says "+/- 10%".  By that metric, it would require 2.97 - 3.63 volts.   Well, it never hurts to try!

I swapped the resistors and took a peek.  Sure enough, it was making signal at a higher peak-to-peak voltage.

The p2p voltage is 2.14 volts, which translates to 11.4 milliwatts.  That's a 25% improvement.  I'll take it!

I'll run the next flight with this modified voltage divider.  I still run some risk as I'm out of spec, and these tests were run at room temperature.  However, nothing ventured, nothing gained!


  1. So the Si5351 has two separate acceptable voltage ranges?